1. Field of the Invention
The invention relates to a needleless injection device with a lower part receiving an agent cartridge and an upper part providing the energy needed for injection; the upper part contains energy store units, namely start unit(s) and supplementary unit(s), capable of elastic form-change; furthermore, the device has a lock maintaining the tension of the energy store units and components to release the lock; and the invention also relates the agent cartridge.
2. Description of Related Art
An advantage of the needleless solutions is that no infection is possible through multiple use of needles or defective sterilization. Another advantage is that agent injection with a needleless device causes a twenty times smaller fracture (an injection hole of cc. 0.008 mm2) on the epidermis than the smallest needle ever used before. Consequently, the needleless solution causes the patient less pain. The agent is prepared in a sterile cartridge, which precisely fits into the injection device. The thrust needed for the injection of the agent is supplied by the expansion of compressed gas as in U.S. Pat. No. 4,913,699, or a mechanical spring structure as used in U.S. Pat. No. 5,190,523. Also known is a solution in which the injection energy is given by the explosion of a suitable detonating charge. The known needleless injection devices usually comprise two parts. One serves for receiving the agent cartridge, while the other is the energy storage unit, where the spring, the compressed gas container, or the explosive capsule is situated. These devices are operated in a way that in the case of a spring, the spring is flexed, and locked in this position. The agent cartridge is inserted, which also contains the piston to discharge the agent. Then the device is positioned on the skin surface with the discharge hole down, and release the energy stored in the energy storage unit. If it works with a spring, the lock is released, in other solutions, the gas capsule is opened, or the explosive is detonated. In each case the released energy thrusts the piston powerfully forwards, and injects the agent stored in the cartridge into the skin, or through the skin into the hypodermic tissues or the muscles. As is known, giving a traditional injection, the doctor thrusts the needle into the desired point with rapid movement, thus opening the way in for the agent. Then, with a moderate push of the syringe, they cause a relatively slow influx of the agent, otherwise the process would be painful and would cause further fraction in the tissues. In injecting the agent, the needleless injection device is expected to perform the same task as expected from a doctor or a nurse in the manual process. To achieve the desired result, the device must be easy to use, that is to say, if it is a spring, it must be easy to flex, it must store sufficient energy, and deliver its energy at a sufficient speed. The injection should not be painful and should cause minimal fraction in the tissues. For the desired spread of this up-to-date device it is indispensable that the device be available for users, including health security institutions, in appropriate quality and at an affordable price. In the case most of the known devices these requirements are not always met completely. The devices, available in patents mentioned above and other marketed products, contain energy storing units capable of injecting agents into the skin, under the skin, into muscles at the requisite speed, but the initiating step of punching the skin, that is corresponding to thrusting the needle with the classic process, is achieved in a way that on releasing, the energy impulse causes a hit-like impact on the piston of the agent cartridge. We know this solution from the specification of WO 03/000319. The released energy first accelerates the piston rod of the energy storing unit, which reaches the cartridge piston with a collision, and only after the collision does the continuous push of the piston begin. The impact exerted by the piston rod of the energy storage unit on the agent cartridge piston will be passed on to the body surface in contact with the device and there causes injuries, suffusion, discoloring and consequent pains.
Some solutions experience with combined spring structure. Although they cannot eliminate the impact on the body, but attempt to achieve certain shock absorption to diminish impact originated injuries, as known from U.S. Pat. No. 4,722,728.
These are based on the concept that the group of springs, as all springs if metal, starts off with a high initial energy, which gradually echoes off. At the moment of dislocking, it produces the impact punching the epidermis, then it empties the agent storage space with linearly decreasing energy, into the body. However, the harmful impact cannot be eliminated with this solution, and it fails to eliminate the described shock absorption effectively. The solution of WO 03/066143 uses also two springs, but they and their effect is not separated one from other. The Patent Specification U.K. 681,098 gives a solution to eliminate most of these problems. It uses a two-stage jet with a hard spring start unit, and separated from it a soft spring for the following injection. For compressing the springs the device is provided with a pull rod, what they have to pull along the long axis of the device with the help of the knob on the top of it. The development efforts are orientated towards an energy storage and release structure which is enabled to store optimal amount of energy and to release it always at the optimal time and speed suitable for fulfilling the task. Too low impact is unsuitable since it causes a partial or complete failure to inject the agent. Perhaps due to a loss or too low a level of energy, the cartridge is not emptied entirely. One of the most important parts of the device is the discharge hole, the precise measure and ideal profile cannot be satisfactorily produced from glass or metal. Thus, for discharge holes, glass cartridges receive metal inlays, metal cartridges receive glass or semiprecious stones (e.g. sapphire or ruby) inlays, the fitting of which into the cartridge raises solidity, while inside the cartridge, owing to turbulences in the joining and contact zones of the metal and the glass, hydrodynamic problems. Although the devices known from patents and available on the market meet the elementary health and technical requirements, they cannot manage the above described quality services. They are also unable to provide the affordable sales price acceptable with disposable devices.